GB2186972A

GB2186972A - Infrared detector

Info

Publication number: GB2186972A
Application number: GB08626507A
Authority: GB
Inventors: Makoto Morimoto; Mikio Kondo
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1986-02-25
Filing date: 1986-11-06
Publication date: 1987-08-26
Also published as: DE3639323C2; AU580898B2; GB2186972B; US4795908A; AU6460486A; GB8626507D0; DE3639323A1

Description

GB 2 186 972 A 1 SPECIFICATION error, and thus can realize accurate

detection of the infrared rays emitted from human bodies or the like Infrared detector object.

According to the present invention, the above aim This invention relates to infrared detectors and, 70 is realized by providing an infrared detectorwhich more particularly, to an infrared detectorwhich incomprises a casing including a base and a coverfit cludes an infrared sensor such as a pyroelectricel- table overthe base, a Fresnel lens mounted to an op ementgenerating a voltage upon incident of infrared ening formed in the cover, a circuit board mounted rays, for detecting the infrared rays originating from on the base and comprising a first part carrying a det an objeetto be detected as condensed by a Fresnel 75 ection-input processing circuit including an infrared lens. sensor positioned at a focal point of the Fresnel lens Because the infrared detector of the type referred and second part carrying a terminal blockfor con to performs its detecting operation in response to in- nection thereto of external lead wires, and means cident infrared rays originating, for example, from allowing infrared rays condensed bythe Fresnel lens human bodies,the detector can be effectively 80 to pass therethrough and mountedtothe basefor utilized in such systems that are for supervising any isolating thefirstpartof the circuit board from the intruderinto a building orthe like where the detector second partof the board andfrornthe ambientairby is installed to inform it, and the like purposes. inhibiting its inflowthereinto.

Generally,there have been proposed various According to such infrared detector of the present types of detection systems wherein an optical sensor 85 invention as arranged as above, the infrared sensor is combined with an optical lens, and one of such which tends to cause an erroneous operation when detection systems is the infrared detector. Disclosed, subjected to a change in temperature condition is re for example, in U.S. Patent No. 4,484,075 to W.G. liably isolated from the ambient air to inhibit air cir Kahl J r. et al. is a detector of the same type in princculation, the detector can perform its infrared recep iple as that of the present i nvention, while this known 90 tion under substantially constant tem peratu re detector is different in a provision of means for irradcondition, and thus a highly precise infrared detec iating lightfrom a light source. That is, in the U.S. tion can be ensured.

Patent, an enclosure has an apertures, a condenser is Other aims and advantages of the present inven provided immediately behind the aperture, and an tion shall be made clear in thefollowing description infrared detecting element is provided on a circuit 95 of the invention detailed with reference to preferred board of a detection-input responsive electronic cir- embodiments shown in accompanying drawings, in cuit, at a focal point of the condenserto receive and which:

detect infrared rays emitted from an objectto be det- Figure 1 is a perspectiveview as disassembled of ected. an infrared detector according to the present inven- The known infrared detector of this U.S. Patent has 100 tion; had several problems in applying itto a detection of Figure2 is a perspectiveview as partially assem such infrared raysthat are emitted from human bled of a cover of the detectorof Figure 1 asviewed bodies. First, since such optical sensorasthe infra- from rearside,with a Fresnel lens mountedthereto; red sensor of pyroelectric type is likelyto cause a det- Figure3is a perpsective view in anotherform of ection error even with a relativelysmall change inthe 105 the Fresne(lens applicabletothe detector of Figure temperature condition,the aperture made in the en- 1; closure of the known detectortendsto allowthe Figure4is a fragmentary sectional viewof a case ambient airto flow intothe enclosureto reachthe of the detector of Figure 1Jor showing a coupled sensorfor causing thetemperature change and thus state of front plate and partition wall defining an iso the detection error. Secondly,the enclosure is requilated chamber; red to have an outletfor lead wires from the circuit Figure 5is a perspective view asfurther assembled board within the enclosure to its exterior, and this of the detector of Figure 1 butwith the cover re outlet also tendsto cause the ambient airtoflow moved; therethrough and even throughoutthe enclosureto Figure 6is a perspective view as still further circulate between the aperture and the outletfor 115 assembled of the detector of Figure 1 and as viewed readily causing the temperature change multi- from an angle differentfrom Figure 5, with the cover plicatively. Further, since the condenser positioned shown as being assembled to the base having other immediately behind the enclosure aperture is ex- elements assembled; posed to the ambient air, the known detector has Figure 7 is a side view showing a state in which the been also defective in thatthe condenser readily be- 120 detector of Figure 1 is mounted against a wall sur comes dustyto lower its optical efficiency, which en- face; tailing in the detection error. Yet, the known detector Figure 8 is a perspective view of a metal fitting has been largely restricted in the installation orienta- used for adjustably mounting the detector of Figure 1 tion and has been thus poor enough in the installato the wall orthe like; tion freedom forfailing in the achievement of precise 125 Figure 9 is a schematic cross-sectional view of the infrared detection when the orientation is improper. detector of Figure 1; A primary aim of the present invention is,there- Figure 10 is a side view showing a state in which fore, to provide an infrared detectorwhich can totally the detector of Figure 1 is mounted differently from eliminate such various problems as have been in- Figure 7; and volved in the prior art to remarkably reduce detection 130 Figure 11 is a schematic cross-sectional view in an-

2 GB 2 186 972 A 2 other embodimentof the detector according to the Zr-Ti alloy. The terminal block 31 has a plurality of present invention. connecting terminals 32 on the front side and wire While the present invention shall now be descri- inserting holes 33 on a lateral side facing the opening bed with reference to the preferred em bodiments 14 of the base 11, the holes 33 corresponding in shown in the drawings, it should be understood that 70 numberto theterminals 32 (see Figure 5). The circuit the intention is notto limitthe invention onlytothe board 28 is mounted onto the base 11 in such that a particular embodiments shown but ratherto cover substantial part 34 of the board forthe detection all alterations, modifications and equivalent arrange- input processing circuit including the infrared sensor ments possible within the scope of appended claims. 29 is housed in a chamber 35 defined bythe partition Referring to Figures 1 to 8, an infrared detector ac- 75 plate and wall parts 15 and 16 of the base 11, whereas cording to the present invention comprises a casing a remaining end part 36 where thd terminal block31 10which includes abase 1 land cover 12. The base is mounted onto the board 28 is extended through 11 has a rectangularframe-shaped body 13which is open side between the engaging grooves 17 and 17a bored at one longitudinal end part of a relatively atthe both ends of the U-shaped partition wall 16 so small area to form an opening 14 and is closed atthe 80 as to occupy part of the opening 14 of the base 11.

remaining area by a partition plate part 15. The body Further provided on the circuit board 28 is an iso 13 isformed to have also a substantially U-shaped lating plate 37 which is engaged at both ends intothe partition wall part 16 erected from peripheral edge grooves 17 and 17a to be disposed between the cir part of the partition plate part 15 except for one edge cuit-carrying substantial part 34 and the terminal part adjacent the opening 14. The partition wall part 85 block-carrying end part 36 of the board for isolating 16 is provided at its both ends adjacentthe opening them from one another. Itwill be appreciated here 14with a pair of opposing engaging grooves 17 and thatthe chamber 35 is surrounded bythe re 17a which extend overthe erected heightof the part- ctangularly provided partition wall part 16 and isolat ition wall part 16, and substantially in the canter of ing plate 37,the latter plate particularly isolating the one longitudinal wall portion with an inward recess 90 chamberfrom the opening 14 of the base 11. Further, 18 in which a plurality of engaging projections 19 are the chamber 35 is covered on the open front side by provided as mutually spaced in the height direction means of a front plate 38which can be air-tightly of the partition wall part 16, while a through hole 20 joined to front side edges of the partition wall part 16 is provided in an upper part of the body 13 at a posi- and isolating plate 37 in such manner as seen in Fig tion corresponding to the recess 18. Further, a hook 95 ures 4-6. While the drawings thefront plate 38 is 21 is provided atthe center of one longitudinal end shown to be joined edgewise to the inner periphery wall of the body 13 defining the opening 14, and an atfront edges of the partition wall part 16 and isolat engaging recess 22 is made preferably in the center ing plate 37, it may be of course possible, if required, of a widthwise wall portion of the partition wall part to prepare the front plate 38to conform ratherto the 16 atthe other longitudinal end of the body 13. 100 outer dimensions atthe front edges of the partition To the back of the body 13, a supplementary base wall part 16 and isolating plate 17, and thus to join 23 of a similarly rectangular dish shape buttrapezothe front plate 38 along its rear side periphery tothe idal in every side view is attached. In the present inst- front edges of the wall part 16 and plate 37. It is desir ance, this supplementary base 23 is coupled to the able in either case to provide a sealing material 39 base 13 preferably as hinged, while not shown, 105 along such joint between the partition wall part and through a thin-walled linkage made along one long- insulating plate 16 and 37 and thefront plate 38 (see itudinal side eges of them, which are lower side in Figure 4). Further, thefront plate 38 has a window40 Figure 1, so thatthe body 13 can take a position tilted expanding in front of the infrared sensor 29 mounted with respectto the supplementary base 23. An angle on thefront side of the circuit board 28, to which adjusting metal fitting 24 generally L-shaped in side 110 window 40 a sheet of filter member 41 isattached.

view is secured atone leg 25to the inner bottom wall With this provision of the front plate 38, in coopera of the supplementary base 23 whilethe other leg 26 tion with the partition plate and wall parts 15 and 16 is extended forward through the through hole 20 in and isolating plate 37 of the base 11, it is ensured that the body 13 (Figures 1 and 8). The metal fitting 24 is the chamber 35 is isolated from the ambient air, so as further provided in extended end part of the other leg 115 notto expose the interior of the chamber 35tothe 26 with a hole 27 into which each of the projections ambient air. Accordingly, no airf low is caused to be 19 on the partition wall part 16 can be engaged so presentwith respectto the detection-input pro that, by engaging suitable one of the projections 19 cessing circuit part 34 including the infrared sensor in the hole 27, a relative angular position of the body 29 on the circuit board 28 and housed within the 13 with respectto the supplementary base 23 can be 120 chamber35, and the detection error occurring dueto adjusted. Respective trapezoidal, peripheral side any change in the ambienttemperature atthe pro walls of the supplementary base 23 are tilted back- cessing circuit can be well restrained. Forthe filter wardly inward, preferably at an angle of 45 degrees. member 41, it is desired to employ a pigment Mounted on thefront side of the base 11 is a circuit containing polyethylene film high in the per board 28 which carries thereon respective elements 125 meabilityto the far infrared rays and also in the of a detection-input processing circuit including an screening effectwith respectto visible rays. Forthe infrared sensor 29, as well as a terminal block31 to pigmentto be mixed in the polyeihylene film, an in which external lead wires 30 are connected. The in- organic compound which can be enumerated is frared sensor 29 may be any known pyroelectric el- titanium oxide, an addition of 0.2-1.0 weight % of ementor, preferably, an element consisting of a Pb- 130 which to polyethylene may suffice the purpose. Asto GB 2 186 972 A 3 its grain size, it has been experimentally known that a lens 47A having a different lens division as shown 0.2-0.3tmwil I resu It in an excellent screening effect in Figure 3 may be employed, as required. Afilter with respect to the visible rays of the central wave member 52 is heat bonded to the front surface of the length (about 0ARm) in the visible range. When the Fresnel lens 47 orthe filter member 52 and the film may be of a white appearance, it may be pos- 70 Fresnel lens 47 are integrally formed during molding sible to mix calcium carbonate orthe like. of the lens 47. The filter member 52 may be made of An operating state indicating lamp 42 is preferably the same material as the filter member 41 ofthefront included in the input processing circuit on the circuit plate 38, that is, the material maybe a sheet high in board 28 to allow the user to visually observe exter- the permeability to the far infrared rays and in the nal ly the operating state of the detector, in which 75 screening effect to any visible rays. In this case, the case a small window 43 having a transparent film incoming infrared rays must pass through the two attached thereto is made in the front plate 38 below filtermembers41 and 52 before reaching the sensor the window 40 at a position opposing the lamp 42. 29 (see Figure 9) and thus visible rays causing erron The cover 12 is generally of a rectangular box eous detection can be remarkably reduced.

shape opened fully on the rear side and fittable atthe 80 In the infrared detector arranged as has been dis opened rear side edges to the front side edges of the closed above according to the present invention,the body 13 surrounding the partition wall part 16 and detection-input processing circuit part 34 of the cir opening 14 of the body 13. In the present instance, cuit board 28 including the infrared sensor 29 is the cover 12 is provided, on an inner peripheral edge housed within the substantially air-tightly isolated part, with a recess (not shown) at a position corchamber35 within the detector casing for effectively responding to the hook 21 of the base 11 for engag- restraining the temperature change due to any ing therein the hook 21 and, on an opposing inner ambient air inflow into the casing, so thatthe infra peripheral edge part, with a projection 44 at a posi- red sensor 29 can perform its detecting operation tion corresponding to the recess 22 of the base 11 for highly accurately, without causing any detection being engaged therein. Fitting the rear open side 90 error in this respect. As the terminal block31 prov edges of the cover 12 thus to the front side edges of ided onto the circuit board 28 is disposed outside the the body13ofthe base ll,with hook21 engagedin isolated chamber 35 so that the terminal-block the corresponding recess and the projection 44 en- carrying part 36 of the board will be in the opening 14 gaged in the recess 22, therefore, the cover 12 can be of the base 11 to be accessible from the rear side,the mounted onto the base 11, enclosing therein the 95 lead wires 30 of the terminal block 31 can be led out input processing circuit in the isolated chamber35 of the detectorwithout any hindrance. Since the and others on the base body 13. Further, the cover 12 Fresnel lens 47 is covered with the filter member 52 has a lens mounting window 45 made in thefront which effectively screens visible rays, the infrared side wall at a position opposed to the window40 of detection can be made highly reliable under a favor the front plate 38, which window45 is provided at its 100 able condition of less presence of the visible rays and upper and lower edges with frontward extended less deterioration in the optical efficiency dueto dust arcuate projections 46 and 46a. A Fresnel lens 47 is orthe like.

mounted to thewindow45tofit along side edgesof In installing the detector of the present invention the window and arcuate edges of the projections46 on a building wall orthe like,the Fresnel lens47 can and 46a. Immediately belowthe window45,the 105 be oriented easily optimumly, aswill be clearfrom cover 12 also has a hole 48 in alignmentwith the Figure 7, even afterfixing of the detectorto thewall lamp 42 and window43, so asto allowthe userto bydriving and fastening screws into the wall surface visually observethe operating state of the indicator through thefixing leg 25 of the adjusting metal fitting 42from the exterior of the cover 12. Desirably, a 24and through the supplementary base 23, sincethe covering piece 49 is slidably mounted insidethe 110 casing 10 can take a desired tilted position byengag cover 12to be adjacent the window 48, for closing ing a desired one of the projections 19 provided on thewindow48 by sliding the piece49 properly. Such the base 11 into the hole 27 of the other leg 26 of the arrangement enables it possible to close the window metal fitting 24, and the detector can realize a highly 48 when it is not desired to allow a third person to accurate detection in this respect, too. Further,the 45 visually observethe indication of the detector's oper115 degrees tilting atthe peripheral side walls of the ating state. Further, such a depressing arm 50that supplementary base 23 is effectiveto allowthe det functions to push a damperswitch (notshown) ectorto be readily installed at a corner of twowalls mounted, for example, on theterminal-block- intersecting at right angles, as shown in Figure 10.

carrying part36 on the circuit board 28 may be prov- The present invention may be modified in various ided onto the innerwall of the cover 12. 120 ways. For example, as will be clearfrom Figure 11 in The Fresnel lens 47 per se may be arranged in any comparison with Figure 9, the partition wall part 116 known manner, for optimumly condensing infrared of the base 111 may befurther extended so thatthe rays incoming in every direction, and focusing them Fresnel lens 147 coated with the filter member 152 through the filter member 41 of the front plate 38 can be directly mounted to the extended end of the upon the infrared sensor 29 on the circuit board 28. In 125 partition wall part 116. In Figure 11, the same mem addition, the Fresnel lens 47 is made slightly larger in bers as those in the foregoing embodiment are den size than thewindow 45 and to be provided at side oted bythe same reference numerals but added by edgeswith hooks 51 and 51 a for reliably firmly secur- 100. Other arrangement and operation are substanti ing the lens to the peripheral edge of the window45. ally the same as those of theforegoing embodiment.

It will be understood that, as the Fresnel lens 47, such 4 GB 2 186 972 A 4

Claims

CLAIMS 7. A detector according to claim 1, wherein said condenser is covered with a filter member.

1. An infrared detector comprising a casing in- 8. A detector according to claim 2, wherein said cluding abase and a cover fittable over said base, a condenser is covered with a filter member attached condenser mounted to an opening formed in said 70 thereto, and said filter member covering said cover, a circuit board mounted on said base and window of said front plate as well as saidfilter comprising a first part carrying a detection-input pro- member covering the condenser are both made of cessing circuit including an infrared sensor posi- identical polyethylene film high in the screening effect tioned atfocal point of said condenser and a second to visible rays.

part carrying a terminal blockfor connection thereto 75 9. A detector according to claim 3, wherein said of external lead wires, and means allowing infrared supplementary base has peripheral side walls which' rays condensed bythe condenserto passthere- are tilted rearwardly inward at an angle of 45 de through and mounted to the basefor isolating said grees.

first part of said circuit board from said second part 10. A detector according to claim 1, wherein said of the board and from the ambient air by inhibiting 80 condenser is a Fresnel lens which is provided at side its inflow. edges with hooks to be engaged to side edges of said

2. A detector according to claim 1, wherein said opening of said cover.

base comprises a bodywhich is opened at one part 11. An infrared detector substantially as descri- to have an opening and closed atthe other remaining bed herein with reference to the drawings.

part by a partition plate part, and a partition wall part erected from said bodyto surround said partition plate partwhile leaving open at an edge adjacent said opening of the bodyfor defining a chamber in Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,7187, D8991685.

which said first part carrying said detection-input Published byThePatentOffice,25 Southampton Buildings, London,WC2A lAY, processing circuit of said circuit board is housed; from which copies maybe obtained.

and said isolating means comprises said partition plate andwall parts of the base, an isolating plate provided at said open edge of the partition wall part for isolating between said first and second parts of the circuit board when the board is mounted on the base with the first part carrying the processing circuit housed within said chamber and the second part carrying theterminal block positioned to extend from the chamber into said opening of the body, and a front platejoined to open front edges of said partition wall part and isolating plateto close thefront side of the chamber and having a window covered by a filter member and positioned in front of said infrared sensor on the first part of the circuit board.

3. A detector according to claim 1, which further comprises a supplementary base disposed on rear side of said base opposite to said cover, said supplementary base being coupled to said base through a hinge connection for rocking motion of the base with respectto the supplementary base.

4. A detector according to claim 3, which further comprises an angle adjusting metal fitting secured at one end to said supplementary base, said metal fitting being provided atthe otherend with an engag- ing means, and said base is provided with a plurality of engaging members mutually spaced infrontward direction of the base for engagement with said engaging means of the metal fitting.

5. A detector according to claim 2, wherein said terminal block includes connecting terminals and wire inserting holes for connecting lead wires respectivelyto each of said connecting terminals, said lead wires connected being led out rearward through said opening of said base.

6. A detector according to claim 2, wherein said partition wall part is provided at both ends parts adjacent said opening of said body with opposing grooves extended in height direction of the wall part, said isolating plate being fitted at both ends in said opposing grooves.